Configurable voltage regulator

ABSTRACT

A configurable semiconductor has a device characteristic that is controllable as a function of at least one external impedance. A measurement circuit measures an electrical characteristic of the at least one external impedance and determines a select value corresponding to the measured electrical characteristic. A first circuit controls the device characteristic as a function of the select value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/602,922, filed Nov. 21, 2006, which is a divisional of U.S. patent application Ser. No. 11/411,377 filed Apr. 26, 2006, which is a divisional of U.S. patent application Ser. No. 11/220,255, filed on Sep. 6, 2005, now U.S. Pat. No. 7,062,392, which is a divisional of application Ser. No. 10/251,372, filed Sep. 19, 2002, now U.S. Pat. No. 6,970,794, the entire contents of which are herein incorporated by reference.

BACKGROUND

Broad classes of semiconductor devices may include several configurations of the same basic device differing in one or more aspects such as output voltage, frequency, trigger temperature, and the like. There are several conventional techniques for providing a specific configuration from a family of devices. In one technique, different versions of the same basic semiconductor are manufactured with slightly different internal component values or configuration to provide the differing outputs. For example, voltage regulators may include a family of devices having various output voltages and tolerance levels. Different devices are manufactured and inventoried by suppliers etc. to provide each of the possible combinations of output voltage and tolerance. An advantage of this approach is that devices with tight tolerances may be provided without the need for expensive external components. However, the cost of the regulators may be higher due to the lower quantities that are produced for each specific voltage/tolerance combination as well as the increased inventory costs.

Another technique uses one or more external components to complete an internal circuit such as an error amplifier for a voltage regulator. Here, the tolerance of the external components has a direct affect on the tolerance of the output that is generated. To attain an output with a tight tolerance, higher priced tight tolerance external components may be required. In addition, a large selection of the tight tolerance external components may be have to be stocked to provide flexibility in setting the output to the desired value.

Shown in FIG. 1A is a third technique for configuring a semiconductor 5. The third technique uses digital input signals to set the semiconductor configuration. Pull-up resistors 6 in combination with switches 7 generate the digital input signals. One digital input may select between two (2¹) configurations. Two digital inputs may select between four (2²) configurations. Three digital inputs may select between eight (2³) configurations and so on. To select between a moderate number of configurations, a large quantity of pins may be required. Dedicating four pins merely for selecting between 16 configurations is costly in terms of both, price and package size. Whereas, using two pins for selection may provide reasonable cost and package size, but only provides selection from amongst four configurations.

SUMMARY

A voltage regulator has a plurality of predetermined configurations and comprises a measurement circuit to measure an electrical characteristic of at least one external impedance and to determine a digital value corresponding to the measured electrical characteristic. An address generator converts the digital value to a first digital address corresponding to a memory location having contents. Each of the contents corresponds to a respective one of the predetermined configurations. A controller configures the voltage regulator based on the contents of the memory location corresponding to the first digital address.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram of a selection circuit connected to a conventional configurable semiconductor.

FIG. 1B is a block diagram of a configurable semiconductor connected to external impedances.

FIG. 2 is a detailed block diagram of a configurable semiconductor connected to external impedances.

FIGS. 3A and 3B are diagrams showing a relationship between an external impedance value and a digital value.

FIG. 4 is a schematic diagram of a configurable semiconductor having a multifunction pin.

FIG. 5 is a schematic diagram of a multifunction pin with programmable control.

FIG. 6 is a schematic diagram of a timing circuit for generating a digital value.

FIG. 7 shows waveforms associated with the timing circuit of FIG. 6.

FIG. 8 is a flow diagram of an operation for configuring a semiconductor.

FIG. 9 is a flow diagram of an operation for selecting values for external impedances for configuring a semiconductor.

FIG. 10A is a block diagram of a voltage regulator connected to an external impedance.

FIG. 10B is a block diagram of a voltage regulator connected to two external impedances.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1B shows a configurable semiconductor device 10 having, for example, two select pins 12 and 14 to connect to two external impedances 16 and 18. The configurable semiconductor device 10 advantageously uses a reduced number of select pins for interfacing to external components, as compared to conventional devices, to select one or more output and internal characteristics. One or more pins may be used to interface to the external component(s). The configurable semiconductor device probes or derives information from the external components connected to the select pins. The derived information has three or more predetermined level ranges that correspond to selected levels of the device characteristics. For example, a single pin connected to an external resistor may be used to select any one of 16 output voltage levels. The resistance of the external resistor is preferably selected to be one of 16 predetermined standard values. Each of the 16 values of resistance corresponds to one of the 16 output voltage levels. In addition, low precision passive components are preferably used as the external components to reduce cost and inventory. Each external component may have multiple, N, predetermined nominal values that each correspond to the selection of a predetermined characteristic level. If one pin is used, then N different characteristic levels may be selected. If two pins are used, then N*N different characteristic levels may be selected, and so forth for an increasing number of selection pins. The types of device characteristics that for example may be selected include output voltage, reference voltage, output current, reference current, clock frequency, temperature threshold, and tolerances of each of the device characteristics. For example, the configurable semiconductor device 10 may have a single select pin 12 connected to an external resistor that may have a nominal value selected from a group of 16 predetermined values. Each of the 16 predetermined values has a measured value range which corresponds to one of 16 predetermined output voltage levels possibly ranging from 3.3 volts to 15 volts. Examples of functional devices for which the configurable semiconductor device is particularly suitable include and are not limited to voltage regulators, current regulators, clock circuits, and temperature sensing circuits.

The external impedances 16 and 18 are preferably resistors, capacitors, or combinations of resistors and capacitors, but may be any component that exhibits predominantly an inductance, resistance, capacitance, or combination thereof. The external impedances 16 and 18 may be connected directly or indirectly from any energy source such as Vdd and ground or any suitable reference to the configurable semiconductor device pins 12 and 14. For example, the external impedance 16 may be connected through a resistor/transistor network to Vdd and through a capacitor network to the select pin 12.

The configurable semiconductor device 10 may determine a predetermined select value corresponding to the measured value of the impedance connected to a select pin. Preferably, the impedance is selected to have a standard value such as nominal resistance values corresponding to resistors having a 10% tolerance (e.g. 470, 560, 680, . . . ) to reduce device and inventory costs. To account for measurement tolerances and the tolerance of the external impedance, a range of impedance values may correspond to a single select value. The select value is preferably a digital value, but may also be an analog value. For example, values of measured resistance from 2400 ohms to 3000 ohms may be associated with a digital value corresponding to 2. While values of measured resistance from 3001 ohms to 4700 ohms are associated with a digital value corresponding to 3. The measured resistance includes variations due to tolerances of the external impedance and the internal measurement circuit. The impedance measured at each select pin is used to determine a corresponding digital value. The range of digital values may include 3 or more digital values and preferably range from 10 to 16 digital values per select pin. The digital values corresponding to each select pin may be used in combination to describe memory addresses. For example, a device having three select pins each to interface to impedance values that are mapped into one of 10 digital values, may describe 1000 memory addresses or lookup table values. The contents of the memory addresses are used to set a value for an output or internal characteristic of the device. Another exemplary device may include two select pins, each configured to interface to external impedances that are mapped to a digital value within a range of 10 values. The digital values in combination may describe 100 memory addresses or lookup table values that may each contain data for setting a characteristic of the configurable semiconductor device.

FIG. 2 shows a block diagram of an aspect of a configurable semiconductor device 20. The configurable semiconductor device 20 includes a select pin 22 to interface to an external impedance 24 that is used for selecting a configuration of the configurable semiconductor device 20. The external impedance 24 is similar in function and scope to the external impedances 16 and 18.

A measurement circuit 26 connected to the select pin 22 measures an electrical characteristic that is a function of the external impedance 24. For example, a current may be supplied to the external impedance and the voltage that is developed across the external impedance 24 then measured. Also, a voltage may be impressed across the external impedance 24 and then measure the current. Any measurement technique for measuring passive components may be used to measure the electrical characteristic including dynamic as well as static techniques. Exemplary measurement techniques include timing circuits, analog to digital converters (ADCs), and digital to analog converters (DACs). Preferably, the measurement circuit has a high dynamic range. The measurement circuit 26 may generate an output having a value corresponding to the value of the external impedance 24. The output may be either digital or analog. The same output value preferably represents a range of external impedance values to compensate for value variations such as tolerances in the external impedance value, interconnect losses, and measurement circuit tolerances due to factors including process, temperature, and power. For example, all measured external impedance values ranging from greater than 22 up to 32 ohms may correlate to a digital output value of “0100”. While measured external impedance values ranging from greater than 32 up to 54 ohms may correlate to a digital output value of “0101”. The actual external impedance values are a subset of the measured external impedance value to account for the value variations. For example, in the above cases the actual external impedance values might be from 24 to 30 ohms and from 36 to 50 ohms. In each case an inexpensive low precision resistor may be selected to have a value centered within the range, such as 27 ohms and 43 ohms. In this way, inexpensive low precision components may be used to select amongst a range of high precision outputs. The select value may be used directly as a variable value to control a device characteristic of the configurable semiconductor 20. The variable value may also be determined indirectly from the select value.

A storage circuit 27 may include variable values that may be selected as a function of the select value. The storage circuit may be any type of storage structure including content addressable memory, static and dynamic memory, and look-up tables.

For the case that the measurement circuit 26 generates output values that have a one-to-one correspondence to the external impedance values, a digital value determiner 28 may then set the output value to a select value that corresponds to a range of external impedance values.

FIG. 3A shows a relationship between groups of impedance values 50 and associated select values 54. The groups of impedance values 50 may have a one-to-one correspondence to groups of digital output values 52 which are converted to the select values 54 associated with each of the groups of impedance values 50. The impedance values ranging from a minimum impedance value to a maximum impedance are separated in into three or more groups, with each group having a nominal impedance. The nominal impedance values of each of the groups may be selected to have a spacing between nominal impedance values. Here, the nominal values, 27 ohms and 43 ohms, of the groups of impedance values have a spacing of 16 ohms. The spacing between the groups of impedance values is preferably based on geometric progression, however any mathematical relationship may be used to establish spacing between the groups such as logarithmic, linear, and exponential. The spacing between impedance groups may be based on any impedance value of the groups including a nominal value, an average value, a mean value, a starting value, and an ending value. Factors that influence selection of the impedance range of the groups and the spacing may include various tolerances such as the tolerance of the external impedance, the tolerance of internal voltage and current sources, and the tolerance of the measurement circuit. The tolerances may for example be caused by process, temperature, and power variations.

FIG. 3B shows a relationship between ranges of impedance values 56 and associated select values 58. The ranges of impedance values 56 have a direct correspondence to the select values 58. The impedance values ranging from a minimum impedance value to a maximum impedance are separated in into three or more groups, with each group having a nominal impedance. The nominal impedance values of each of the groups may be selected to have a spacing between nominal impedance values. Here, the nominal values, 27 ohms and 43 ohms, of the groups of impedance values have a spacing of 16 ohms. This direct correspondence between the ranges of impedance values 56 and associated select values 58 may be implemented by, for example, a nonlinear analog to digital converter (not shown).

Referring back to FIG. 2, an address generator 30 may determine memory locations corresponding to the digital output values associated with external impedances connected to the select pins. The memory locations may be grouped in any manner such as a list for a single select pin, a lookup table for two select pins, and a third order table for three select pins.

A controller 32 sets a device characteristic of the configurable semiconductor device 20 as a function of the variable value. The variable value may be generated directly by the measurement circuit, determined indirectly from the select value, and determined from the contents of a memory location corresponding to the external impedance values connected to the select pins.

FIG. 4 shows an aspect of another configurable semiconductor device 60. Configurable semiconductor device 60 is similar to configurable semiconductor device 20 in function, except that configurable semiconductor device 60 includes at least one multi-purpose select pin 62. The multi-purpose select pin 62 may be used for configuring the semiconductor device 60 as well as for an additional function such as power down (PD), power enable, mode selection, reset, and synchronous operation. The semiconductor device 60 may be configured in a manner similar to that of configurable semiconductor device 20.

In one aspect, a first range of impedance values connected to the multi-purpose select pin 62 may be used to configure the configurable semiconductor device 60, while operation of the additional function may be controlled by a voltage or current impressed on the multi-purpose select pin, or impedance values outside the first range of impedance values.

An external impedance 64 and a switch 66 may be connected to the multi-purpose select pin 62 to provide the selection function and the additional function respectively. Bias voltages, Vb1 and Vb2, may be applied to the external impedance 64 and transistor 66. The bias voltages, Vb1 and Vb2, may each be any value ranging from negative voltage through ground to positive voltage, and equal or not equal. The switch 66 may be connected in any manner including from the multi-purpose select pin 62 to ground, from the multi-purpose select pin 62 to a voltage source, from the multi-purpose select pin 62 to a current source, and from the multi-purpose select pin 62 through another impedance to an energy source. Any type of switch or device configured as a switch may be used including transistors, analog switches, jumper wires/traces, and manual switches.

FIG. 5 shows a configurable semiconductor device 70 coupled to a digital control circuit 72. The digital control circuit 72 may be connected in any manner such as a stand-alone circuit and included in another device such as a processor. The configurable semiconductor device may include a multi-purpose select pin 74 similar in function to configurable semiconductor device 60. The digital control circuit 72 may include several switches 76 to control external impedances 78 for setting an impedance on the multi-purpose select pin 74. Any number and type of switches 76 may be employed including transistors, analog switches, jumper wires/traces, and manual switches. Preferably, the external impedances 78 are selected to have standard values although any range of values may be used. Another transistor 80 may control operation of additional functions.

FIG. 6 shows one embodiment of a measurement circuit 100 for determining a digital output 106 corresponding to an external impedance 102. The external impedance 102 may be connected to the measurement circuit 100 through a select pin 104. Table I shows exemplary values for the external impedance 102 and corresponding values of the digital output. Predefined operation #2 may enable the power down function. The impedance at the select pin that corresponds to predefined operations #1 or #2 may be intentional or unintentional such as a selected resistor, a cold solder joint, a broken trace, shorted traces, or a failed external device.

TABLE I Digital # Rx/Ry Vout Vout % Output 0 Short to Vss up 0 0 Predefined to 10k operation #1 1 19.6k  0.8 −2 000 2 28.5k  1.0 −4 001 3  40k 1.2 −6 010 4  56k 1.5 −8 011 5 80.6k  1.8 +2 100 6 113k 2.5 +4 101 7 160k 3.0 +6 110 8 226k 3.3 +8 111 9 400k to an open Predefined operation #2

FIG. 7 shows a timing diagram associated with the measurement circuit 100. A first waveform 120 represents a clock signal 120 to the D flip-flop 110. A second waveform 122 represents an input signal to the D input of the flip-flop 110. In operation, a controlled resistor 112 is initially set to a predetermined value. A first voltage is developed at a first node 114 as a function of the controlled resistor 112 and the external impedance 102. The first voltage is clocked through the flip-flop 110 by the clock signal 120. An incrementer/decrementer 116 may convert the output of the flip-flop 110 to the digital output 106. In response to the digital output 106, a decoder 118 adjusts the controlled resistor 112 to decrease the first voltage. The counter continues to increment until the first voltage decreases to a level equivalent to a logic “0”.

FIG. 8 shows an operation of a configurable semiconductor device. Starting at block 150, energy is supplied to an external impedance. Continuing to block 152, an electrical characteristic that is a function of the external impedance is measured. Electrical characteristics such as a voltage at the select pin and a current flowing through the select pin may be measured. At block 154, a select value corresponding to the measured electrical characteristic is determined. Continuing to block 156, an address may be generated as a function of the digital value. At block 158, the contents of the address are determined. At block 160, a variable may be controlled as a function of the select value such as directly and based on the address contents. At block 162, a device characteristic such as an output voltage may be controlled as a function of the variable.

FIG. 9 shows an operation for selecting the spacing of external impedances used for configuring a semiconductor device. The spacing is preferably selected to permit the use of low precision components by varying the spacing from lower values to higher values to account for potential variations associated with the measurement circuit. Starting at block 200, a measurement circuit is provided. Continuing to blocks 202 and 203, tolerances associated with the measurement circuit and the external impedances may be determined. The tolerances may include variations due to process, temperature, and power. At block 204, a measurement error such as a geometric progression, a maximum error, and root of the sum of the squares (RSS) error may be computed. Continuing to block 206, a quantity of discrete values for the external impedance may be determined. For example, the measurement error may be applied across a voltage range of the measurement circuit to determine the maximum number of discrete values that may be selected. The quantity of discrete values may be any integer value greater than one. At block 208, nominal values are selected for the external impedance as a function of the computed error and the selected quantity of discrete values. The described operation is not limited to the described order of operation. Other ones of the variables may be solved for such as solving for the tolerance of the external impedance after selecting a desired quantity of discrete values.

FIG. 10A is an example of a voltage regulator in accordance with the present invention. Referring now to FIG. 10A a voltage regulator 200 is shown therein providing Vout to load 210, an external impedance 220 is used to select Vout. Table II shows exemplary values for the external impedance 220 and corresponding values of Vout. Predefined operation #2 may enable the power down function or low voltage to protect for an overvoltage condition presented to load 210. The impedance at the select pin that corresponds to predefined operations #1 or #2 may be intentional or unintentional such as a selected resistor, a cold solder joint, a broken trace, shorted traces, or a failed external device.

TABLE II # Impedance 220 Vout 0 Short to Vss up 0 or power to 10k down 1 19.6k  0.8 2 28.5k  1.0 3  40k 1.2 4  56k 1.5 5 80.6k  1.8 6 113k 2.5 7 160k 3.0 8 226k 3.3 9 400k to an open 0 or low voltage

FIG. 10B is an example of a voltage regulator in accordance with the present invention. Referring now to FIG. 10B a voltage regulator 200 is shown therein providing Vout to load 210, an external impedance 220 is used to select a nominal Vout and impedance 240 is used to select the offset from the nominal Vout. This provides for a significant number of additional output voltages. Table III shows exemplary values for the external impedance 220 and corresponding values of the offset percentages. If impedance 240 is a large value or perhaps an open circuit no offset will be applied to the nominal Vout. While if impedance 240 is a short or very low a predefined operation, such as discussed above, is implemented.

TABLE III Offset # Impedance 240 percentage 0 Short to Vss up Predefined to 10k operation 1 19.6k  −2 2 28.5k  −4 3  40k −6 4  56k −8 5 80.6k  +2 6 113k +4 7 160k +6 8 226k +8 9 400k to an open No Offset

TABLE IV Imped 240 Short to Vss up to 10k 19.6k 28.5k 40k 56k 80.6k 113k 160k 226k 400k to Imped Nominal Offset % an 220 Vout 0 −2 −4 −6 −8 +2 +4 +6 +8 open Short 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or to Vss power power power power power power power power power power power power up to down down down down down down down down down down down down  10k 19.6k  0.8 0.8 * 0.784 0.768 0.752 0.736 0.816 0.832 0.848 .0864 0.8 28.5k  1.0 1.0 * 0.980 0.960 0.940 0.920 1.020 1.040 1.060 1.080 1.0  40k 1.2 1.2 * 1.176 1.152 1.128 1.104 1.224 1.248 1.272 1.296 1.2  56k 1.5 1.5 * 1.470 1.440 1.410 1.380 1.530 1.560 1.590 1.620 1.5 80.6k  1.8 1.8 * 1.764 1.728 1.692 1.656 1.836 1.872 1.908 1.944 1.8 113k 2.5 2.5 * 2.450 2.400 2.350 2.300 2.550 2.600 2.650 2.700 2.5 160k 3.0 3.0 * 2.940 2.880 2.820 2.760 3.060 3.120 3.180 3.240 3.0 226k 3.3 3.3 * 3.234 3.168 3.102 3.036 3.366 3.432 3.498 3.564 3.3 400k 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or 0 or to an low low low low low low low low low low low low open voltage voltage voltage voltage voltage voltage voltage voltage voltage voltage voltage voltage * predefined operation

Table IV above is an example of the nominal Vout and the offset percentage selected in accordance with external impedances. For example if impedance 220 is nominally 160 k ohms the nominal Vout is 3.0 volts and if impedance 240 is 28.5 k the offset from the nominal Vout is −4%. This results in a Vout of the voltage regulator of 3.168 volts.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims. 

1. A configurable semiconductor, comprising: N terminals adapted to be connected to at least one of T external impedances, where N is an integer greater than zero and T is an integer greater than one, wherein said T external impedances have impedance values within predetermined tolerances; a measurement circuit that measures an impedance value of said at least one of said T external impedances; and a control circuit that compares said measured impedance value to T ranges and that selects a value of a device characteristic based on said comparison, wherein said value of said device characteristic selected by said control circuit is independent of said predetermined tolerances of said T external impedances.
 2. The configurable semiconductor of claim 1 wherein one of said T ranges is defined by an upper range value that is greater than or equal to an upper tolerance value of said at least one of said T external impedances.
 3. The configurable semiconductor of claim 2 wherein said one of said T ranges is defined by a lower range value that is less than or equal to a lower tolerance value of said one of said T external impedances.
 4. The configurable semiconductor of claim 1 wherein said T ranges are each defined by an upper range value that is greater than or equal to an upper tolerance value of a corresponding one of said T external impedances.
 5. The configurable semiconductor of claim 4 wherein said T ranges are each defined by a lower range value that is less than or equal to an lower tolerance value of a corresponding one of said T external impedances.
 6. The configurable semiconductor of claim 1 wherein said device characteristic is selected from a group consisting of output voltage, reference voltage, output current, reference current, clock frequency, a temperature threshold and a device tolerance.
 7. A device comprising said configurable semiconductor of claim 1 wherein said device is selected from a group consisting of voltage regulator, a current regulator, a clock circuit and a temperature sensing circuit.
 8. The configurable semiconductor of claim 1 wherein said device characteristic comprises an internal characteristic.
 9. The configurable semiconductor of claim 1 wherein said device characteristic comprises an output characteristic.
 10. The configurable semiconductor of claim 5 wherein said upper range value of a first one of said T ranges is less than or equal to said lower range value of an adjacent second one of said T ranges and wherein said lower range value of said first one of said T ranges is greater than or equal to said upper range value of an adjacent third one of said T ranges.
 11. The configurable semiconductor of claim 1 wherein said T ranges correspond to T address values, respectively, and further comprising: an address generator that selects one of said T address values based on said measured impedance value.
 12. The configurable semiconductor of claim 11 wherein said value of said device characteristic is stored at a memory location that is selected based on said one of said T address values.
 13. The configurable semiconductor of claim 1 further comprising a generator that supplies power to said at least one of T external impedances during measurement.
 14. The configurable semiconductor of claim 1 wherein said measurement circuit is selected from a group consisting of a timing circuit, a digital to analog converter, and an analog to digital converter.
 15. The configurable semiconductor of claim 1 wherein each of said T external impedances are selected from a group comprising a capacitance, an inductance, a resistance and combinations thereof.
 16. A method for configuring a semiconductor, comprising: adapting N terminals of a semiconductor to be connected to at least one of T external impedances, where N is an integer greater than zero and T is an integer greater than one, wherein said T external impedances have impedance values within predetermined tolerances; measuring an impedance value of said at least one of said T external impedances; comparing said measured impedance value to T ranges; and selecting a value of a device characteristic based on said comparison, wherein said value of said device characteristic selected by said control circuit is independent of said predetermined tolerances of said T external impedances.
 17. The method of claim 16 further comprising defining one of said T ranges by an upper range value that is greater than or equal to an upper tolerance value of said at least one of said T external impedances.
 18. The method of claim 17 further comprising defining said one of said T ranges by a lower range value that is less than or equal to a lower tolerance value of said one of said T external impedances.
 19. The method of claim 16 further comprising defining each of said T ranges by an upper range value that is greater than or equal to an upper tolerance value of a corresponding one of said T external impedances.
 20. The method of claim 19 further comprising defining each of said T ranges by a lower range value that is less than or equal to an lower tolerance value of a corresponding one of said T external impedances.
 21. The method of claim 16 further comprising selecting said device characteristic from a group consisting of output voltage, reference voltage, output current, reference current, clock frequency, a temperature threshold and a device tolerance.
 22. The method of claim 16 further comprising selecting said device from a group consisting of voltage regulator, a current regulator, a clock circuit and a temperature sensing circuit.
 23. The method of claim 16 wherein said device characteristic comprises an internal characteristic.
 24. The method of claim 16 wherein said device characteristic comprises an output characteristic.
 25. The method of claim 20 further comprising: selecting said upper range value of a first one of said T ranges to be less than or equal to said lower range value of an adjacent second one of said T ranges; and selecting said lower range value of said first one of said T ranges to be greater than or equal to said upper range value of an adjacent third one of said T ranges.
 26. The method of claim 16 further comprising: selecting said T ranges to correspond with T address values, respectively; and selecting one of said T address values based on said measured impedance value.
 27. The method of claim 26 further comprising storing said value of said device characteristic at a memory location that is selected based on said one of said T address values.
 28. The method of claim 16 further comprising supplying power to said at least one of T external impedances during measurement.
 29. The method of claim 16 further comprising selecting each of said T external impedances from a group comprising a capacitance, an inductance, a resistance and combinations thereof. 